sorry if this isnt the right place to post this but ive looked for help elsewhere and found nothing. 

One of my cities bordering a coast was sieged by an enemy on one land tile that was only accessible through the city (walled off by siege) and otherwise bordered only by water. it was impossible to attack them because land armies couldnt reach the destination and ships couldnt attack from the water. eventually they moved into the water and i defeated them but now a dozen or so turns later, the city is still walled off and considered under siege even though no enemy is anywhere nearby. 

i saw some similar posts like this on other forums but they were from years ago and had no solutions.